How do I convert things into moles?? Help...?

Question

The problem:
How many molecules is in each of the following?
1.50 X 10^23 molecules NH3

I just need help to solve one and then I can do the rest on my own. How do I solve this equation?
These are the others:
1 billion (1 X 10^9) molecules O2
6.02 X 10^22 molecules Br2
4.81 X 10^24 atoms Li

so the second one would be 1 X 10^31?
I took the equation (1 X 10^9) given and just divided it by the mole equation. Does the number of oxygens or something count or is that for a different equation type?

Answer 1

1 mole contains 6.022x10^23 molecules

1.50x10^23/6.022x10^23 = 0.25 moles of NH3

Answer 2

Just say to yourself 1000 times
" One mole of a compound or one g-atom of an element is 6.02x10^23 molecules or atoms."
All of these can be solved by proportion. Example
1/6.02x10^23 = X/1.50x10^23 (1st problem)
X= 0.25 moles.

Answer 3

there are 6.022*10-23 atoms/molecules in a mole of any substance